Damper system for synchronous generators



Nov. 12, 1946.

R. RUDENBERG DAMPER SYSTEM FOR SYNCHRONOUS GENERATORS Filed Dec. 31,1942 6 Sheets-Sheet l XII/I4 s\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ vlnvemor.

REINHOLD R DENBERG By. M1 WMMM AHy.

1946- R. RUDENBERG 2,411,002

DAMPER SYSTEM FOR SYNCHRONOUS GENERATORS Filed Dec. 51, 1942 6Sheets-Sheet 2 FIG.4I FIG.5

lnvemor.

REINHOLD RUDENBERG I AHy.

Nov. 12, 1946. R. RUDENBERG DAMPER SYSTEM FOR SYNCHRONOUS GENERATORSFiled Dec. 31, 1942 6 Sheets-Sheet 3 time curreni FIG.IO

L Ida CH lnvenror. REINHOLD RUDENBERG NOV. 12, 1946. RUDENBERG 2,411,002

DAMPER SYSTEM FOR SYNCHRONOUS GENERATORS Filed Dec. 31; 1942 6Sheets-Sheet 4 FIG.I8

Nov. 12, 1946. R. RUDENBERG DAMPER SYSTEM FOR SYNCHRONOUS GENERATORSFiled Dec. 31, 1942 6 Sheets-Sheet 5 FIG.22

FIG.23

FIG.24

lnven+or REINHOLD R"DEN BERG NOV. 12, 1946. RRUDENBERG 2,411,002

DAMPER SYSTEM FOR SYNCHRONOUS GENERATORS Filed Dec. 31, 1942 6Sheets-Sheet 6 as 1s msz 76 I 79 FIG. 27 3O guuu uuu uu uuu uifl F |G.29L30 lnvenror.

REINHOLD RU ENBERG By. (WW M AH y.

Patented Nov. 12, 1946 UNITED STATES PATENT QFFICE DAMPER SYSTEM FORSYNCHRONOUS GENERATORS Reinhold Rudenberg, Belmont, Mass.

Application December 31, 1942, Serial No. 470,867

16 Claims. 1

The invention relates to synchronous electrical machines both of thesalient and the cylindrical pole types and its objects are new.arrangements of the damping circuits on the rotors of thesemachines,.damping circuits, which, while they ensure perfect operationof such synchronous machines especially generators or alternators undernormal and abnormal conditions, in addition thereto, suppress or reducein magnitude those :large .initial over-currents which arise in case ofsudden short-circuits in the lines, especially such short-circuits whichoccur near the terminals of the machine, effects which with the usualdamping circuits cannot be controlled.

More specifically, this invention is concerned with'the arrangement ofdamper circuits on the rotors of said machines and the establishment of.a certain definite relationship between said dampercircuits andspecific magnetic fields of a synchronous electrical machine. Thesemagnetic fields are (l) the magnetic main field on a path in the directaxis of the rotor, (2) the magnetic main field on a path in thequadrature axis of the rotor, (3) the magnetic leakage field in theirect axis of the rotor and closed on a bypath between the poles of eachpair of field poles, and (4) the magnetic leakage field in the quadatureaxis of the rotor and closed .on a bypath transverselyto each of thefieldipo'les; the term bypath as :herein employed being more specifical-'ly explained and defined hereinafter.

In the following specification these four mag- .neticfields respectivelywill be understood when the shorter terms (1) direct axis main field,(2) quadrature axis main field, (3) direct axis leakage :fi'eld, (4)quadrature axis leakage field, are used.

It is the primary object of this invention to bring the aforesaid fourmagnetic fields and the damping circuits upon, and closed within, therotor mutually into a relationship so as to obtain the full dampingeffect of the damper circuits on the direct axis and quadrature axismain fields whereas the two leakage fields or at least the vdirectaxisleakage field mayfiuctuate freely.

To'this end, the invention specifically provides for a mutualarrangement of the electric and magnetic circuits of the machine,specifically of the rotor dampercircuits and of the bypath of at leastthe magnetic leakage field in the direct axis of .the rotor, whichresults in a weak linkage of said circuits compared with the linkage ofsaid dam-percircuits with the'paths of both magnetic main'-fie-lds-direct axis and quadrature axis fields.

More specifically, the magnetic and elec- 55 trio characteristics ofsaid damper circuits and of the bypaths of both leakage fields, or atleast of the magnetic leakage field in the direct axis of the rotor, areadjusted so as to result in a time constant of the fluctuations of saidleakage fields or field, which is smaller thanone-half the period of thealternating current of the network to which the machine is connected.

By this means, the damper circuits of the invention, in the same way asthe known damper circuits will aiiect the direct aids field and willprevent over-voltage in the field exciting machine if this excite! is ofhigh self-inductance, and, in any case, in the field winding if thiswinding is accidentally opened. Since the quadrature axis field islikewise clamped by damper circuits of the invention, the new machinemay carryany unsymmetrical or single-phase load and any hunting of themachine caused by disturbances during its operation will be suppressed.

In contradistinction to the known machines,

however, in a machine of this invention, the direct axis leakage flux,as it is not closely linked with damping circuits, is free to fluctuateand can develop freely when short-circuit currents occur.

This freely fluctuating direct axis leakage flux will therefore decreasethe magnitude of these short-circuit currents. In certain embodiments ofthe invention tobe used preferably in case of large quadrature axisarmature reaction, as for instance, with turbo-alternators of thecylindrical rotor type, provision is made that the quadrature axisleakage fiux may likewise fluctuateiireely and thus further decrease themagniture of short-circuit currents in the stator.

Further objects of the invention and various of its embodiments will beset forth in the specification as it proceeds and be illustrated in andby the accompanying drawings which are to be understood exp'licative ofthe invention and not limitative of its scope. Other embodimentsincorporating the principle underlying my invention are feasible withoutdeparting from the spirit and ambit of my appended claims.

In the drawings:

Fig. 1 illustrates a side elevation, partly in section, along the linel! of 2, of a synchronous generator of the salient pole type with a poleshoe damper system and a bobbin damp-er system of this invention mountedon the rotor;

Fig. 2 is a front elevation, partly in section, along the line 2-2 ofFig. 1, of the same machine;

Fig. .3 is a longitudinal view, partly in section, along the line 33 ofFig. l, of a'cylindrical rotor provided with a slot damper system inaccordance with this invention, and

Fig. 4 is a cross section, along the line 4-4 of Fig. 3, of this rotorshowing the slots of the rotor, its field and damper windings;

Fig. 5 shows the cross section of a modified rotor slot with damper bar,on an enlarged scale;

Figs. 6 and '7 show diagrammatically and in elevation a section of themagnetic frame of a salient pole machine of the type of Figs. 1 and 2and illustrate schematically the location of the paths of the fourmagnetic fields of the machine;

Figs. 8 and 9 show corresponding views of the location of the paths ofthe four magnetic fields in the case of a machine with cylindricalrotor;

Figs. 10 to 13 are diagrams showing the development of the terms timeconstant and linkage;

Fig. 14 is a scheme for illustrating the computation of the magnitude ofthe time constant of a machine;

Figs. 15 and 17 show an elevational section respectively along the lines15-45 and II-l'l of Figs. 16 and 18, and

Figs. 16 and 18 a top view of a pole pair each provided with amodification of the damper systems illustrated in Fig. 1;

Fig. 19 represents on an enlarged scale and in section part of thebobbin damper of Fig. 17;

Fig. 20 is a longitudinal section, along the line 20-28 of Fig. 21; and

Fig. 21 a cross section, along the line 2l2l of Fig. 20 of amodification of the pole shoe damping system of Figs. 1 and 2;

Fig. 22 is a longitudinal section of the body of a cylindrical rotorprovided with circumferential slits for adjusting the electric andmagnetic characteristics of the eddy current paths;

Fig. 23 is a longitudinal elevation of a pole provided withcircumferential slits and oblique slits at the side faces;

Fig. 24 shows a diagrammatic side view of a pole provided with damperwindings in the pole shoe at a distance from the pole shoe surface;

Fig. 25 shows a longitudinal elevation partly in section, along the line25-25 of Fig. 26, and

Fig. 26 a side view of a pole provided with two damper system andcircumferential slits as another embodiment of the invention;

Fig, 27 illustrates diagrammatically a rotor slot with its excitingwindings together with a diagram of the slot leakage flux in the directaxis;

Fig. 28 shows diagrammatically a slot with damper winding together witha diagram of the slot leakage flux in the quadrature axis;

Fig. 29 is a longitudinal section, along the line 29-23 of Fig. 30, and

Fig. 30 a cross section, along the line B l-30 of the iron body of acylindrical rotor provided with circumferential lits, a damper system atthe slot bottoms, and an additional damper system in slots arranged inthe center parts of the poles.

In Figs. 1, 2, 6, and '7, the stator of the machine is designated by H,its rotor by 12, both separated from each other by an air gap 29. Thefield poles l8, 19, mounted on, or solidary with, the rotor core 23, areprovided with exoiter Windings 2i fed from any conventional source ofdirect current through the collector rings 22,

The stator H is provided in the usual manner with armature windings 23arranged in slots 25 between teeth 25, and connected through theterminals 26 to an alternating current network.

A cylindrical rotor is shown in Figs. 3, 4, 8, and

4 9. Its core is designated by 30, the field poles by 28 and 29. Fieldwindings 3! are embedded in slots 32 between teeth 36 and are securedwithin the slots by wedges 33, the end connectors 34 of the fieldwindings being held against the action of the centrifugal force by endbells 35.

For the purpose of not obscuring or crowding the aspect of my drawings,I have omitted in the following figures details not essential to theexplanation of my invention. As a stator has been illustrated in Figs. 1and 2, I have indicated the stator only schematically in Figs. 6 to 9,whereas, in the other figures, the tator has been omitted. Instead ofcomplete rotors I have shown in some instances only single poles or onepair of poles, In some figures I have omitted from the showing the fieldwindings. It will be readily understood therefore that for the actualcarrying out of complete machines embodying my invention, these omitteddetails may be easily supplemented by any one familiar with theconstruction of synchronous machines.

In order to define clearly the terms which I use in the followingspecification and claims, I have shown in the diagrammatic views ofFigs. 6 to 9 for a given position of the rotor schematically thelocation of the paths of the four magnetic fields which I haveenumerated above.

The paths of the four magnetic fields are indicated by dashed lines Hi,l5, I5, and II, respectively. l4 represents (Figs. 6 and 8) the path ofthe magnetic main field produced by the exciter winding 2| of the fieldpoles 18, as, Figs. 1 and 2, or the exciter winding 3! of the fieldpoles 28, 29, Figs. 3 and 4. This path is in the direct axis of therotor, traverses the stator teeth 25 and windings 23, (Fig. 2), therotor core 53, Fig. 2, or 30, Fig. 4, twice the air gap 2i], and isclosed through the armature or stator frame II. It indicates (Figs. 7and 9) the path of the magnetic main field produced by the armaturewinding 23 in the quadrature axis of the rotor. This path traverses thestator core H, the stator teeth 25 and windings, Fig, 2, twice the airgap 29, the interpole space or quadrature axis of the rotor pole systemand the rotor core l3 (Fig. 7 or 1), or 30 (Fig, 9 or 2).

15 illustrates the path of themagnetic leakage field in the direct axisof the rotor. This path traverses the pole ends 31, twice the air gap20, the stator teeth 25 and windings 23, and is closed in the rotorspaceon a path between the field poles 1'8 and 19, Fig. 6 or 28 and 29,Fig. 8. Since, as the diagrams Figs, 6 and 8 illustrate, this pathbetween the field poles closes the magnetic leakage field in the directaxis of the rotor on a bypath to the main field in the direct axis, Ishall, in order to designate this path and to distinguish it from themain path of this field, employ in this specification and in the claimsfor this path the term bypath on the rotor which closes the magneticleakage field in the direct axis between the field poles.

l1, finally, shows the path of the magnetic leakage field in thequadrature axis of the rotor. This path traverses the stator teeth 25and windings 23, twice the air gap 20, and is closed in the rotor spaceon a path transversely of each field pole I8 and I9, respectively, inFig. 7, or 28 and 29, respectively, in Fig. 9. Since, as the diagramsFigs. 7 and 9 illustrate, this path transversely of the field, polescloses the magnetic leakage field in the quadrature axis of the rotor ona bypath to the main field in the quadrature axis, I shall, in order todesignate this path and to distinguish it from the main path of thisfield, employ in this specification and in the claims for this path the.term bypath which closeson the rotor the magnetic leakage Jfield in thequadrature axis transversely of the field poles? The paths of themagnetic main fields and of the magnetic leakage fields in thedirectaxis and thosein the quadrature .axis jhave respectively been .shown intwo separate figures, viz. Figs. 6

and '7 for a salient pole type machine and in Figs. .8 and 9 'for acylindrical rotortype machine. IThis separate showing. is f or thepurpose of clearness .only, it is obvious, however, these .fourmagneticfields are simultaneously present and are thus tobe consideredsimultaneouslyin any synchronous machine.

Figs. 10 to .14 are drawnior theexplanation of the terms period, timeconstant, and flinkage.

1. PERIOD (a) Expressed by changc with time I have shown in Fig, 10 inthe conventional way the curve of an alternating current and'indicatedby P its .fperlod that is the time after which repetition ofuthephenomenon occurs.

(12) Determined by the data of the synchronous machine The period may beexpressed by the numberp .of pole=pairs andthenumber of revolutions persecond as 1 number =0f 'pole-pairsXnumber of revolutions ;per second 2.TIME CONSrAN'r (a) Expressed by change with time lam air T Therefore,the time constant is given-as A4) deviation.from -fina1 value .offiuxd/dt' or rate of-change of fiux (b) Determined by circuit and fieldOhmic resistance R and self-inductance Lot anelectric circuitlinked'with the magnetic field under consideration determine the timeconstant-of this electromagnetic field as self-inductance ,L T=1 OIresistance (0) Several time constants Electric circuits or magneticfields may have two or even more time constants. This is shown,

for example,.in Fig. 12 .where the time constant T1 may be-that of .amain fieldand Tathat of a leakage field.

3. LINKAGE The intensity of the "electromagnetic interaction between anelectric circuit and a magnetic field is expressed by the linkage.

As shown at Fig. 13 weak linkage of a damper circuit with a field pathmay be attained by:

(i) Placing the damper circuit out of the full range of the field thefluctuations of which may beproduced by stator currents.

(ii) Increasing the self-inductance L of the damper circuit,

(iii) Increasing the resistance R of the damper circuit.

Since the fiux linked with the damper circuit contributes to theself-inductance, means (i) and (iii) result in a small time constant Inthe usual damper circuits, if their resistance and their .inherentinductance are sufiiciently small, the damper currents, closed inthemselves, will prevent by interaction the fluctuation of any magneticfields in .the rotor including those which rotate synchronously with therotor. In case of a sudden development of short circuit currentsin thestator winding, the usual damper will therefore prevent or considerablydelay any rapid transient Variation of the direct axis leakage fiux. Itis therefore the effect only of the stator leakage which will limit themagnitude of the initial short-circuit current.

If, however, in accordance with my invention, the damper circuits are soarranged that their linkage with the .bypaths of both the leakage fieldin the direct axis of the rotor and the leakage field in the quadratureaxis of the rotor, or at least with the bypath of the leakage field inthe directaxis of'the rotor, is weak compared with the linkage of saiddamper circuits with the paths of both magnetic main fields, the dampercircuits will retain all the useful damping effects on the main fieldsrevolving with the rotor or over the rotor, while, for instance, as inthe case of a sudden short-circuit of the statorwinding, anydetrimentaleffect on the leakage fiuxes in both axes of the rotor or at least inthe direct axis of the rotor is avoided.

Thus, for instance, if the rotor leakage in the direct axis of a certainmachine is of the value of the stator leakage, the initial magnitude ofthe sudden short circuit currents will be reduced to when the machine isprovided with the dampers of this invention.

Generally, with my new dampers the initial value of the suddenshort-circuit currents is determined no longer by the leakage of thestator alone but by the value of the total of stator and rotor leakages.

The optimum effect of the damper circuits of my invention will bereached when the magnetic and electric characteristics of the dampercircuits, namely their self-inductance and their electric resistance.and the magnetic resistance of the bypaths of both magnetic leakagefields or at least the bypath of the magnetic leakage field in thedirect axis of the rotor are adjusted so to result in a time constant ofthe fluctuations of both said magnetic leakage fields or at least thatin the direct axis, respectively, smaller than half the period of thealternating current as will be shown later on.

.In the case where the linkage of the damper circuits with the "bypathsof both the magnetic leakage field in the direct axis andthat in thequadrature axis of the rotor are weak compared with the linkage of saiddamper circuits with the paths of both magnetic main fields, thereluctances of both said bypaths, including possible reluctances of anyend connectors of the windings, in a preferred embodiment of theinvention, are adjusted to substantially. the same values. Generally,the reluctance R is determined by wherein Z is the length, a thecross-sectional area of the path, and a the permeability. Since the pathis composed of magnetic lengths and air lengths, in the evaluation ofthe reluctance, with the conventional methods and taking intoconsideration of these parts, it is obvious that the reluctances of theiron lengths in the bypaths are negligible against the air lengths.

For all practical purposes, therefore, the aforesaid condition may alsobe expressed: The lengths of the bypaths in'air over the mean crosssections of the bypaths in air are to be laid out to have substantiallythe same value for both the bypath which closes the magnetic leakagefield on the rotor in the direct axis and the bypath which closes themagnetic leakage field on the rotor in the quadrature axis.

In terms of space, the principles upon which the design of the dampercircuits of this invention'will be based, are as follows:

The direct axis damper circuits will be arranged remote from the air gapbetween rotor and stator, since the direct axis leakage field alwaysflows in those parts of the rotor which are adjacent to the air gap.Thus, the direct axis damper will not be situated above the fieldwinding, as has been the usual practice up to now, but it will belocated within or below the zone of the field winding.

The quadrature axis damper may also be disposed below the zone of thefield winding and may possibly be combined with the direct axis damperto a complete damper cage. Or, a quadrature axis damper may be locatedwithin the field winding or above the field winding or at both places,provided the damper is so disposed that sufficient quadrature axisleakage flux may flow between armature winding and damper, and providedthat the damper is not linked with the direct axis leakage flux. Thedamper is, for example, not linked with the direct axis leakage flux ifits axial conductors are located at the center pole lines.

The magnetic and electric characteristics of 1e machine may becalculated by the usual methods in order to adjust them so as to obtainthe desired time constant of the fluctuations. Furthermore, if desired,certain steps may be taken subsequently, after completion of themachine, by means of which the results actually obtained may becorrected or adjusted.

If, for instance. the core of the rotor is of solid magnetic steel, eddycurrents may occur. The time constants of these eddy currents which dampthe direct axis leakage field, or the quadrature axis leakage field, orboth, may then be not small enough compared with half the period of thestator alternating current.

These damping effects may, however, be reduced to the desired values if,in accordance with another feature of the invention, circumferentialslits are provided within the zone of the bypartner the direct axisleakage field, orof the quadrature axis leakage. field or of both.

Fig. 14 illustrates schematically how in an actual machine the timeconstant of a leakage flux may be computed from an equivalentarrangement, sufficiently accurate in most of the cases practicallyoccurring.

The paths of both the direct and quadrature axes leakag fluxes mayconsist of' several steel parts, as for example the rotor teeth in Fig.4, of several air gaps, forv instance the rotor slots 32 and additionalthereto the gap between stator and rotor, for instance 2!], and oflaminated steel parts provided by the stator iron which closes themagnetic circuit.

In the equivalent schemeof Fig. 14, the total of the lengths of thesolid iron paths is indicated by c and of the air paths by d. Let a andb be the equivalent cross sections of the solid mag netic path, the eddycurrent time constant of such a scheme, as shown in principle in Fig.14, may then be computed from the dimensions a, b, c, and d, as

where s is the specific electric resistance of the solid steel parts.

In the embodiment of the invention shown in Figs. 1 and 2, the salientpole rotor is provided with two systems of dampers. One system comprisesdamper windings 4!, 42, 413, closed about, and coaxially with, thequadrature axis and is disposed within the field poles 2! in proximityto the air gap surfaces of the field poles i8 and 19.

The second damper system comprise damper windings upon the field polesclosed about, and coaxially with, the direct axis. and disposed inspaced relation to the air gap 28.

The first system, the damper for the quadrature axis main flux, consistsof bars 4| embedded in slots in the center of the pole shoes 21 andclosed by end conductor rings 62, 43 at both axial faces of the'rotor.Each pair of adjacent bars 4| and the sectors of the rings 52, asconnecting them, form a single short-circuited turn which surroundscoaxially the quadrature axis in the interpole space. This winding islinked only with the quadrature axis flux, and not with any main flux orleakage flux in the direct axis of the poles. Since this position of thebars 4! is symmetrical to the direct axis flux, this flux does notinfluence the damper and thus all the bars may be connected by theconducting end rings 42, 43 to a one-bar-per-pole cage. Since the barsare in a neutral position in relation to the direct axis fluxes, thebars need not be insulated from the steel poles, a fact which greatlyfacilitates the construction. v

The second system, the damper for the direct axis main flux, is a frameM of copper or other conductive material surrounding the pole core. Thisframe 44 may be used, as the drawings show, simultaneously as a bobbinfor the field coils 2i, and will thus be generally of L-shape crosssection. Frame l t-therefore, forms a damper circuit linked with themain fiux only but not, or only weakly, with the leakage flux in thedirect aXis of the rotor. This leakage flux in the direct axis of therotor may therefore vary freely with any fluctuation of the armaturecurrent.

Figs. 2, 6 and '7 show that the linkage of the damper circuits for thedirect axis main flux with the bypath of the magnetic leakage field inthe direct axis of the rotor is weak compared with the linkage of thedamper circuits with the paths of the main magnetic field in the directaxis. The damper circuits for the quadrature axis are linked only withquadrature axis fields.

Machines of this invention will be designed with regard to the magneticand electric characteristics of the damper circuits and of the bypathsof the two magnetic leakage fields, or at least of the leakage field inthe direct axis, or the characteristics of the bypa'ths and the dampercircuits will be so adjusted with regard to each other, that, resultingfrom this design or adjustment, the time constants of the fluctuationsof the magnetic leakage field in the direct axis and in the quadratureaxis, or at least the time constant of the fluctuations of the leakagefield in the direct axis is smaller than half the period of thealternating current.

The embodiment of the invention illustrated in Figs. and 16, shows thedamper circuits for the direct ams main field in form of coil bobbinscc, disposed remote from the air gap and substantially outside of thebypath of the direct axis leakage field.

The quadrature axis damper system consists of a number of turns 46, 41,48, insulated by tubes 49 and embedded into slots 59 near the face ofthe pole shoe and closed on the faces of the rotor. They form individualshort-circuited turns coaxial with the quadrature axis in the interpolespace. These turns may consist of one bar each or of any number of wiresof conductive material. They are linked only with the quadrature axesfiuxes and not with any main or leakage fluxes in the direct axis of thepoles.

In the example shown in Figs. 17, 18, and 19, damper circuits for thedirect axis main field comprise short-circuited turns 53 insertedbetween layers of the field winding 54, whereas the bobbins 55 mayeither be of insulating or poorly conducting material or may likewise beused as a damper of the direct axis main field. The shortcircuited ordamper turns 53, when the field winding is wound of flat copper strips,as indicated in the drawing, may be formed by brazing, soldering orwelding together a few consecutive turns of the field winding which thenare left without insulation. These short-circuited turns may also bearranged only at the lower part of the pole, leaving the upper part ofthe pole free for the fluctuations of the direct axis leakage field.

The poles are further provided near their pole shoe surfaces 53 with aone-barper-pole cage consisting of uninsulated bars 59 of conductivematerial connected to a cage by ring sectors as at the faces of therotor. The bars 59 are embedded within slots 6] tapering towards thepole faces and opening thereto with a narrow slit 62.

Figs. and 21 illustrate a pole which is long in the axial direction ofthe rotor. In this case; end connectors for the single damper bars inthe pole shoes may be dispensed with if the uninsulated bars are firmlyseated within their slots 65. The slots of these bars may again beclosed as-Fig. 15 shows, or they may be open and form narrow slits 6!above the damper bars 65 as in Figs. 20 and 21. These figures illustrateby means of the arrows the flow of the damper currents within the polesand from pole to pole.

In turbo-alternators with cylindrical rotors, the rotor slots areusually closed by means of wedges of brass or a similar material of hightensile strength and high electric conductivity. In machines of thisinvention, however, the axial overall conductance of the wedges is to bereduced,

10 for instance, by providing non-magnetic or evenmagnetic steel wedges(33 in Figs. 4 and 5) or Wedges of some other poorly conductivematerial. In this way free fluctuations of the rotor leakage fiuxes in atransverse direction through the slots are made possible.

Figs. 3 and 4 illustrate the rotor slot damper system of this inventionwhich is to replace the usual damper constituted by conductive wedges ofthe rotor. 7

Bars 10 of copper or other highly conductive material and of appropriateform, are embedded within the slots 32 at their bottom. The damper barsare connected to a cage by means of conductive end rings 1! connectingthe axial ends of the damper bars at either side of the rotor. Thedamper cage thus formed is perfectly linked with the magnetic mainfluxes of both the direct and quadrature axes.

In the modification shown in Fig. 5, conductive bars 73 tapered andflattened towards the bottom of slots 32 are embedded within separatesemi-closed grooves 12 underneath, and opening into, the slots 32. Thebars of the rotor in this modification are electrically orconductivelyconnected with one another by being fitted closely within their grooves12 and thus giving good contact with the steel body of the rotor. Thebars may be forced plastically into their grooves after the contactingsurfaces had been thoroughly cleaned.

For turbo-generators with cylindrical rotors it will be expedient toreduce the damper effect also on the quadrature axis flux to such an ex-'1, 27, the slot leakage flux in the quadrature axis does not decreasetowards the bottom and its distribution is rather rectangular asillustrated in Fig. 28. It may therefore be useful to fill slots 16, asshown in Figs. 29 and 30, in the center part 82 of the pole pieces,partially or entire- 1y, with damper bars 77 in order to adjust themagnitude of the quadrature leakage flux,

The influence of such damper bars, as dashed line 19 shows, decreasesthe distribution of the resultant flux towards the bottom of the slot.This resultant flux is indicated by the densely shaded part of thediagram.

Bars 11 may be of copper or other conductive material, The slots 76 maybe closed at their tops with wedges 18 of magnetic material whereas theother slots 32 may be closed by wedges 83 of non-magnetic material.

The bottom dampers 79' are perfectly linked with the direct axis mainfield and the quadrature axis main field but only weakly linked with thedirect axis and the quadrature axis leakage fluxes. Bars 11 are in aposition neutral to the direct axis fluxes, they are, however, linkedwith the quadrature axis main flux, but weakly linked with thequadrature axis leakage flux. By appropriately choosing, and harmonizingwith each other, dimensions, positions, and other characteristics ofboth dampers, any desired damping effect may be set or adjusted.

If the rotor is built up partly or entirely of solid steel, the overalllongitudinal conductance of the wedges may be reduced for instance byreplacing the conductive wedges through poorly conductive steel wedges,or by subdividing copper or brass wedges into short lengths. Eddy l lcurrents will thus develop mainly in the rotor body. These eddycurrents, in spite of the specific resistance of the rotor body, maycause considerable damping eifects because of the large cross-sectionsofiered to these currents. These damping effects may be adapted to thepurposes of this invention, the more so, if by the means offered by thisinvention the eddy currents are limited as to their magnitude and theplaces where they occur, They may then cooperate with the dampers orreplace them in part.

In accordance with the invention, the damping eddy currents may bereduced in their magnitude or uppressed to such an extent that thedirect axis leakage flux is enabled to fluctuate freely by beingrelieved from the linkage with eddy currents. Furthermore, it willsufiice to weaken this linkage only to an extent that the time constantis small enough to enable the leakage flux to follow the ascent of anyshortcircuit current suddenly originating in the stator winding. Thisascent or variation will occur in half a period of the alternatingcurrent and the invention provides therefore an adjustment of themagnetic and electric characteristics of the damper circuits and of thebypath of the two leakage fields or of at least the magnetic leakagefields in the direct axis so as to result in time constants of thefluctuations of the two leakage fields, or ofat least the magneticleakage field in the direct axis, smaller than half the period of thealternating current.

Fig. 22 shows how this object of adjusting the magnitude of the eddycurrents and determining or restricting the place or places where theyoccur, may be attained by circumferential slits of appropriatedimensions. These slits 86 may be extended over the whole circumferenceof the rotor, as Figs. 29 and 30 show. They subdivide the eddy currentpaths along the teeth 8i, the pole pieces 82, and the wedges 83 of theslots 32. The resistance of the eddy current paths within the zones ofthe leakage paths may thus be increased and the linkage and timeconstant reduced to the desired values.

In the embodiment of a turbo-alternator illustrated in Figs. 29 and 30various features of this invention have been combined. Non-magneticsteel wedges 83 hold the field coils; circumferential slits 86 throughteeth 8i, wedges 83 and pole pieces 82 reduce the leakage time constantsin both axes, so as to prevent any substantial damper action at and nearthe pole faces; slotbottom copper dampers l ensure direct axis andquadrature axis main flux time constants of sumcient magnitude; andslots 16 at the pole centers, closed by magnetic steel wedges F8 for asmooth magnetic surface and partially filled with copper bars ll adjustthe quadrature am's leakage flux to the direct axis leakage flux of theslots and of the end windings of the rotor.

Fig. 23 shows the same principles applied to solid poles 18 ofsalient-pole synchronous machines. It is sufficient in most cases togroove circumferential slits 85 in the pole shoes only, down to a depthwhich subdivides an appropriate cross-section for the free fluctuationof the leakage fluxes flowing within the poles. In order to enable theleakage field fluctuations also to enter the axial ends of the poleshoes, these too may be appropriately subdivided by axial slits as at85.

The most balanced reaction on the currents in the armature inding willbe obtained when the free rotor leakage fluxes in both the direct axisand the quadrature axis are made equal or when the reluctances of boththeir bypaths are adjusted to substantially the same values. This can beachieved in salient pole machines by a proper adjustment in space of thedirect axis and the quadrature axis damper systems so as to obtain equalfree leakage fluxes in both axes.

In cylindrical rotors this object may be achieved by suitably adjustingslot-bottom dampers; width and depth of central pole slots and ofcentral pole bars; forms, depths, widths, and spacing of circumferentialslits.

Fig. 24 shows an example how for this purpose by choosing appropriatelythe depths of theslits 88 above the pole bars, the total quadrature axisflux may be subdivided, in an arbitrary proportion, into a damped mainpart within the cage formed by the damper system 36, 7, 8, and anon-damped leakage part without the cage.

Figs. 25 and 26 show another embodiment of the invention with bobbindampers d4, furthermore, pole bar dampers M connected with one anotherat the faces of the rotor by means of U or V shaped end connectors 89mounted by means of pins or bars 90 at the spider E3 of the rotor. Suchconnectors, by their increased leakage, permit a certain amount of thequadrature flux to fluctuate freely. In order to enable the quadratureaxis leakage flux to vary in the solid part of the pole, the pole shoe2'! is provided with circumferential slits extended below the dampersbars 6! Synchronous machines built with the damper circuits of this.invention will develop initial short-circuit currents which are muchsmaller than those developed in machines with ordinary squirrel-cage orpole-cage dampers. In machines of this invention the rotor leakagereactance will participate to its full value in limiting the initialshort-circuit peak, and, in addition thereto, owing to the reducedmagnitude of this peak, a stator leakage reactance will result whichthrough the lower resultant saturation is considerably greater than thatwhich may be obtained with ordinary dampers.

Since through the dampers of this invention the magnitude of theshort-circuit currents may be reduced towards one half, power stations,the maximum capacity of which is limited preponderantly by the magnitudeof the initial short-circuit currents, may now be designed with up totwice the former capacity.

I claim:

1. In a synchronous generator, a rotor having a field system includingpoles and field windings surrounding said poles for producing a magneticfield in the direct axis of said field system; said rotor further havingdamper circuits about the direct axis and damper circuits about thequadrature axis of said field system; said damper circuits about thedirect axis, to the exclusion of any direct axis damper system near theperipheral faces of said poles, disposed in spaced relation to saidperipheral pole faces and substantially within the rotor spacesurrounded by the peripheral zone comprising the bypaths which close themagnetic leakage fields on said rotor respectively between andtransversely of said field poles.

2. A synchronous generator as set forth in claim 1 wherein both saiddamper circuits are disposed in spaced relation to said peripheral polefaces and substantially within the rotor space surrounded by theperipheral zone comprising the bypaths closing the magnetic leakagefields on l3 said rotor respectively between and transversely of saidfield poles.

3. A synchronous generator as set forth in claim 1 wherein both saiddamper circuits are disposed in spaced relation to said peripheral polefaces and substantially within the rotor space surrounded by theperipheral zone comprising the by-paths closing respectively themagnetic leakage field in the direct axis between said field poles andthe magnetic leakage field in the quadrature axis transversely of eachof said field poles, and wherein the lengths of the bypaths in air overthe mean cross sections of the bypaths in air are laid out to havesubstantially the same value for both the bypath which closes themagnetic leakage field on said rotor in the direct axis and the bypath.which closes the magnetic field on said rotor in the quadrature axis.

4. In a synchronous generator, a rotor, at least the core of said rotorbeing of magnetic steel admitting of the formation of damping eddycurrents, said rotor, having afield system including poles and fieldwindings surrounding said poles for producing a magnetic field in thedirect axis of said field system, said rotor further having dampercircuits about the direct axis and damper circuits about the quadratureaxis thereof; said damper circuits about the direct axis, to theexclusion of any direct axis damper system near the peripheral faces ofsaid poles, disposed in spaced relation to said peripheral pole facesand substantially within the rotor space surrounded by the peripheralZone comprising the bypaths closing respectively the leakage field inthe direct axis between said field poles and the leakage field in thequadrature axis transversely of each of said field poles; said rotorbeing provided, at least within said bypath which closes the leakagefield of the direct axis, with slits not reaching substantially deeperthan the depth of said bypath for shaping the magnetic and electricconfiguration of said bypath so as to reduce the magnetic time constantof said damping eddy currents to a value smaller than half the period ofthe alternating current of the network to whi h said synchronous machineis to be connected.

5. A synchronous generator as set forth in calim 4 wherein said rotorwithin said bypath of said leakage field in the direct axis is providedwith circumferential slits not reaching substantially deeper than thedepth of said bypath.

6. A synchronous generator as set forth in claim 4 wherein said rotorwithin both said .bypaths is provided with circumferential slits notreaching substantially deeper than the depths of said bypaths.

'7. In a synchronous generator, a rotor, field poles upon said rotor,field windings upon said field poles, said rotor having damper circuitsabout the direct ELXiS and damper circuits about the quadrature axisthereof; said damper circuits including, to the exclusion of any directaxis damper system near the peripheral faces of said poles, damperwindings disposed about the direct axis of said rotor and in spacedrelation to said peripheral pole faces substantially within the rotorspace surrounded by the peripheral zone comprising the bypaths closingthe magnetic leakage fields on said rotor respectively between andtransversely of said field poles; said damper circuits further includingdamper windings individually closed about and coaxial with saidquadrature axis and disposed within said field poles in proximity to theperipheral faces of said field poles,

8. In a synchronous generator, a rotor having a field system includingpoles and field windings surrounding said poles for producing a magneticfield in the direct axis-of said field system; said rotor further havingdamper circuits thereon and closed within said rotor, said dampercircuits, to the exclusion of any direct axis damper system near theperipheral faces of said poles, including single bars longitudinallydisposed in the center planes of said field poles and connectorsdisposed at thev axial faces of said rotor, said bars and saidconnectors forming av one-bar-per-pole cage upon said rotor..

9. A synchronous generator as set forth in claim 1 wherein said dampercircuits about the direct axis include short circuited turns of saidfield windings, inserted between layers of said field windings.

10. In a synchronous turbo-generator, a cylindrical rotor, field poleson said rotor, said field poles having teeth and slots located.therebetween, fieldi windings disposed Within said slots, said rotorhaving damper circuits about the direct axis and damper circuits aboutthe quadrature axis thereof; said damper circuits about the direct axis,to the exclusion of any direct axis damper system near the peripheralfaces of said field poles, disposed in spaced relation to thecylindrical surface of said rotor and substantially within the rotorspace surrounded by the peripheral zone comprising the by-paths closingthe magnetic leakage fields on said rotor respectively between andtransversely of said field poles.

11. In a synchronous turbo-alternator, a cylindrical rotor, field poleson said rotor, said field poles having teeth and slots locatedtherebetween, field windings disposed within said slots and wedges forclosing said slots, damper circuits upon and closed within said rotor;said damper circuits, to the exclusion of any direct axis damper systemnear the peripheral faces of said poles, including a damper windingcomprising bars of highly conductive material disposed exclusively atthe bottoms of said slots and conductive elements for electricallyconnecting said bars to one another.

12. In a synchronous turbo-alternator, a cylindrical rotor, field poleson said rotor, said field poles having teeth and slots locatedtherebetween, field windings disposed within said slots and Wedges forclosing said slots, damper circuits upon and closed within said rotor;said damper circuits, to the exclusion of any direct axis damper systemnear the peripheral faces of said poles, including a damper windingcomprising bars of highly conductive material disposed exclusively atthe bottoms of said slots and peripheral conductors at least at theaxial terminals of said bars and conductively secured thereto.

13. In a synchronous turbo-alternator, a cylindrical rotor, field poleson said rotor, said field poles having teeth and slots locatedtherebetween, field windings disposed within said slots and wedges forclosing said slots, damper circuits upon and closed within said rotor;said damper circuits, to the exclusion of any direct axis damper systemnear the peripheral faces of said poles, including a damper windingcomprising bars of highly conductive material disposed exclusively atthe bottoms of said slots and, at least at the axial terminals of saidbars, conductively secured to the body of said rotor.

14. In a synchronous turbo-alternator, a cylindrical rotor, at least thecore of said rotor being of solid magnetic steel admitting of theformation of eddy currents, field poles on said rotor, saidfield poleshaving teeth and slots located therebetween, field windings disposedwithin said slots and metallic wedges for closing said slots, dampercircuits upon and closed within said rotor; said damper circuits, to theexclusion of any direct axis damper system near the peripheral faces ofsaid poles, including a damper winding comprising bars of highlyconductive material disposed exclusively at the bottoms of said slotsand conductive elements at least at the axial terminals of said bars forconductively connecting to one another said bars; said rotor within atleast the bypath which closes the magnetic leakage field in the directaxis between said field poles provided with circumferential slits, saidcircumferential slits extended toand not substantially surpassing theroots of said teeth, thus subdividing said teeth and said wedges.

15. In a synchronous generator, a rotor having a field system includingsalient poles and field windings surrounding said salient poles forproducing a magnetic field in the direct axis of said field system, saidrotor further having damper circuits about the direct axis and dampercircuits about the quadratureaxis of said field system; said dampercircuits about the direct axis, to the exclusion of any direct axisdamper system near the peripheral faces of said poles, including framesof conductive material and of L-shaped cross section disposed about saidsalient field poles.

16. A synchronous turbo-generator as set forth in claim 10 wherein saidgenerator is laid out as to self-inductance 0f the damper circuits,electric resistance of the damper circuits, and magnetic resistance ofat least the bypath which closes, on said rotor, the magnetic leakagefield in the direct axis, so as to result at normal operation of saidgeneratorin a time constant of the fluctuations of at least said lastnamed leakage field smaller than half the period of the alternatingcurrent of the network to which said turbogenerator is to be connected.

REINHOLD RUDENBERG.

